ADENOVIRAL E1B-55KDA PROTEIN INHIBITS YEAST MESSENGER-RNA EXPORT AND PERTURBS NUCLEAR-STRUCTURE

The mechanisms of export of RNA from the nucleus are poorly understood ; however, several viral proteins modulate nucleocytoplasmic transport of mRNA. Among these are the adenoviral proteins E1B-55kDa and E4-34k Da. Late in infection, these proteins inhibit export of host transcrip ts and promote export of viral mRNA. To investigate the mechanism by w hich these proteins act, we have expressed them in Saccharomyces cerev isiae. Overexpression of either or both proteins has no obvious effect on cell. growth. By contrast, overexpression of E1B-55kDa bearing a n uclear localization signal (NLS) dramatically inhibits cell growth. In this situation, the NLS-E1B-55kDa protein is localized to the nuclear periphery, fibrous material is seen in the nucleoplasm, and poly(A)() RNA accumulates in the nucleus, Simultaneous overexpression of E4-34 kDa bearing or lacking an NLS does not modify these effects. We discus s the mechanisms of selective mRNA transport.